This invention relates to subsea pipeline connections and in particular to an apparatus for connecting a horizontally extending flowline to a vertically extending production riser.
It is common practice today when completing underwater wells to run flowlines from various wellheads along the seabed to a remotely located production facility. The production facility will normally include a plurality of production risers to which the flowlines must be connected.
When remote flowline installation methods are used, it is usually required that some form of seal be remotely set between the connecting point at the riser and the flowline. For this purpose a stroking action of one of the mating ends is required. While the flowline must be pulled to bring it into an initial position, stroking of the flowline for sealing purposes is unreliable since a large portion of the flowline must be moved each time and the force requirements will be erratic.
Therefore, it has been conventional to stroke the riser end of the connection. This has been accomplished by the use of flexible loops which accommodate the stroking motion by flexing of the loops. This requires a relatively large loop pipe section and stroking takes considerable force where the size of the connecting pipe is large. It also takes considerable space since enough length must be allowed to permit the required movement of the stroked flange without overstraining the flexing pipe.
Alternatively, use has been made of a slip joint where stroking is permitted by one tubular member sliding within a second member with a seal between the two. This relies on sliding type seals at a location where replacement is relatively difficult. Such seals are less reliable than a straight compression seal because of the sliding and potential rolling action on the seal itself.